java - 无法将 json 数据添加到 ArrayList 中

Question

我试图在 listView 中显示来自 JSON 的数据，但每当我尝试从 json 添加一些值时，我的列表都不会显示任何内容。

Activity

public static final String LOG = hourlyWeather.class.getSimpleName();
    double test;
    RequestQueue mQuene;
    ArrayList<Weather> list;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_hourly_weather);
        mQuene =  Volley.newRequestQueue(this);

        list = new ArrayList<Weather>();
        test();

        hourlyWeatherAdapter adapter = new hourlyWeatherAdapter(this, list);

        ListView listView = (ListView) findViewById(R.id.weatherListView);

        listView.setAdapter(adapter);
    }
    public void test() {
        String url = "https://api.openweathermap.org/data/2.5/weather?lat=50.7578594&lon=16.2127653&units=metric&appid=ID";
        JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET, url, null,
                response -> {
                    try {
                        JSONObject object = response.getJSONObject("main");
                        for (int i = 0; i<object.length(); i++){
                            test = object.getDouble("temp");
                        }
                        Log.i(LOG,String.valueOf(test));
                        list.add(new Weather(test));

                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }, Throwable::printStackTrace);
        mQuene.add(request);
    }
}

适配器

public class hourlyWeatherAdapter extends ArrayAdapter<Weather> {

public hourlyWeatherAdapter(@NonNull Context context, ArrayList<Weather> list) {
    super(context, 0, list);
}
@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {

    View view = convertView;
    if (view == null) {
        view = LayoutInflater.from(getContext()).inflate(R.layout.weather_list_item, parent, false);
    }
    Weather model = getItem(position);

    TextView temperature = (TextView) view.findViewById(R.id.hourly_time);
    temperature.append(String.valueOf(model.getTemp()));

    return view;
 } 
}

public class Weather {

private double temp;

public Weather(double temp) {
    this.temp = temp;
}

public double getTemp() {
    return temp;
 }
}

当我使用 Log.i 时，我可以清楚地看到 logcat 中 json 的值。哪里可以出问题？我尝试添加一些虚拟数据，效果很好。

Answer 1

您必须在 onCreate() 方法外部声明 hourlyWeatherAdapter adapter = new hourlyWeatherAdapter(this, list);，并且在更改数组后，必须调用 notifyDataSetChanged();。此外，您必须在调用 test() 之前初始化列表和适配器。

public static final String LOG = hourlyWeather.class.getSimpleName();
    double test;
    RequestQueue mQuene;
    ArrayList<Weather> list;
    hourlyWeatherAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_hourly_weather);
        mQuene =  Volley.newRequestQueue(this);

        list = new ArrayList<Weather>();
        adapter = new hourlyWeatherAdapter(this, list);

        ListView listView = (ListView) findViewById(R.id.weatherListView);
        listView.setAdapter(adapter);

        test();
    }

    public void test() {
        String url = "https://api.openweathermap.org/data/2.5/weather?lat=50.7578594&lon=16.2127653&units=metric&appid=ID";
        JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET, url, null,
            response -> {
                try {
                    JSONObject object = response.getJSONObject("main");
                    for (int i = 0; i<object.length(); i++){
                        test = object.getDouble("temp");
                    }
                    Log.i(LOG,String.valueOf(test));
                    list.add(new Weather(test));

                    // Update list
                    adapter.notifyDataSetChanged();

                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }, Throwable::printStackTrace);
       mQuene.add(request);
    }
}